In modern integrated circuits, a huge number of individual circuit elements, such as field effect transistors, are formed on a single chip area. Typically, feature sizes of these circuit elements are reduced with the introduction of every new circuit generation, to provide currently available integrated circuits with high performance in terms of speed and/or power consumption. A reduction in size of transistors is an important aspect in steadily improving device performance of complex integrated circuits, such as CPUs. The reduction in size commonly brings about an increased switching speed, thereby enhancing signal processing performance.
At reduced sizes, field effect transistors may exhibit poor linearity for use as amplifiers. The linearity of transistor amplifiers is poor because the drain current of a transistor is a nonlinear, power-law function of its gate-to-source voltage. The mechanisms that produce this undesirable trait are inherent in the fundamental physical properties of field effect transistors. Nonlinearity of transistor amplifiers is generally due to transconductance (gm) nonlinearity in the driving transistor. Linearity of radio frequency (RF) devices is important because non-linearity introduces many problems, including gain compression, cross modulation and intermodulation.
In contrast to conventional planar metal-oxide-semiconductor field effect transistors, multiple gate (“multigate”) transistors incorporate two or more gates into a single device. Relative to single gate transistors, multigate transistors reduce off-state current leakage, increase on-state current flow, and reduce overall power consumption. Multigate devices having non-planar topographies also tend to be more compact than conventional planar transistors and consequently permit higher device densities to be achieved.
One known type of non-planar, multigate transistor, commonly referred to as a “finFET,” includes two or more parallel fins (“fin structures”) formed on a substrate, such as a silicon-on-insulator substrate. The fin structures extend along a first axis between common source and drain electrodes. At least one conductive gate structure is formed over the fin structures and extends along a second axis generally perpendicular to the first axis. More specifically, the gate extends across and over the fin structures such that an intermediate region of the gate conformally overlays three surfaces of each fin (i.e., an upper surface, a first sidewall surface, and a second opposing sidewall surface of each fin). The surfaces form the channel of the gate.
While providing the advantages noted above, conventional finFETs also exhibit poor linearity for use as amplifiers. Accordingly, it is desirable to provide integrated circuits and methods for fabricating integrated circuits with transistor devices having improved linearity for used as amplifiers. Also, it is desirable to provide integrated circuits and methods for fabricating integrated circuits including multiple gate devices with dual threshold voltages. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.